The Ukraine crisis has shone a spotlight on one of the glaring gaps in the world: the lack of a strategic and purposeful Europe. The United States can and should lead on the response to this conflict, but nothing can really happen without Europe. The European Union is by far Russia’s largest trading partner — it buys much of Russia’s energy, is the major investor in Russian companies and is the largest destination for Russian capital. Some of President Obama’s critics want him to scold Vladimir Putin. But ultimately, it is European actions that the Russian president will worry about.

Consider how Europe has dealt with Ukraine. For years, it could not really decide whether it wanted to encourage Ukrainian membership in the union, so it sent mixed signals to Kiev, which had the initial effect of disappointing pro-European Ukrainians, angering Russians and confusing everyone else.

In 2008, after Moscow sent troops into Georgia, Europe promised an “Eastern partnership” to the countries along Europe’s eastern fringe. But, as Neil MacFarlane and Anand Menon point out in the current issue of the journal Survival, “The Eastern partnership was a classic example of the EU’s proclivity for responding to events by adding long-term and rhetorically impressive, but resource-poor, bolt-ons to existing policy.”

European leaders were beginning to woo Ukraine without recognizing how this would be perceived in Russia. Moscow had its own plans for a customs union, to be followed by a Eurasian Union, which was meant to be a counter to the European Union. Ukraine was vital to Russia’s plans and was dependent on Russia for cheap natural gas. Plus, of course, Ukrainians were divided over whether to move west or east.

Negotiations between the European Union and Ukraine for an association agreement meandered along, with the lawyers and translators taking a year to work out the text. In describing this tardiness as a mistake, Polish Foreign Minister Radoslaw Sikorski said, “The same thing applies to the [European] Union as to the Vatican. God’s mills grind slowly but surely.” The deal that was offered to Ukraine was full of demands for reform and restructuring of its corrupt economy, but it had little in the way of aid to soften the blows and sweeten the pot. When then-President Viktor Yanukovych rejected Europe’s offer and sided with Moscow, he set in motion a high-speed, high-stakes game that Europe was utterly unprepared for and could not respond to.

If Europe was trying to move Ukraine into its camp, it should have been more generous to Kiev and negotiated seriously with Moscow to assuage its concerns. Instead, Europe seemed to act almost unaware of the strategic consequences of its actions. Then when Russia began a campaign to destabilize Ukraine — which persists to this day — Europe remained a step behind, internally conflicted and unwilling to assert itself clearly and quickly. Those same qualities have been on display following the downing of Malaysia Airlines Flight 17.

The European Union still has a chance to send a much clearer signal to Ukraine, Russia and the world. It could demand that Russia pressure the separatists to cooperate fully with the investigation of Flight 17 and allow the Ukrainian government — which Moscow recognizes — to take control of its own territory in eastern Ukraine. It could put forward a list of specific sanctions that would be implemented were those conditions not met within, say, two weeks.

In addition, Europe should announce longer-term plans on two fronts, first to gain greater energy independence from Russian oil and gas. European nations must also reverse a two-decade downward spiral in defense spending that has made the E.U. a paper tiger in geopolitical terms. Germany, for example, spends about 1.5 percent of its gross domestic product on defense, among the lowest rates in Europe and well below the 2 percent that is the target for all NATO members. It’s hard for a country’s voice to be heard and feared when it speaks softly and carries a twig.

The problem is now being described as European cowardice and appeasement. It is better explained by an absence of coherence among the European Union’s 28 very different countries, a lack of strategic direction and a parochial inward orientation that looks for the world’s problems to go away. The result is a great global vacuum, with terrible consequences.

If we look back years from now and wonder why the liberal, open, rule-based international order weakened and eroded, we might well note that the world’s most powerful political and economic unit, the European Union, with a population and economy larger than America’s, was the great no-show on the international stage.